1. Field of the Invention
The present invention generally relates to hard disk drives (HDDs), and more particularly to methods and apparatus for electrically detecting predetermined surface characteristics on magnetic read/write heads, such as head slider surface imperfections and contamination.
2. Description of the Related Art
Disk drives using magnetic recording of digital information store most of the information in contemporary computer systems. A disk drive has at least one rotating disk with discrete concentric tracks of data. Each disk drive also has at least one recording head typically having a separate write element and read element for writing and reading the data on the tracks. The recording head is constructed on a head slider and the head slider is attached to a suspension. The combination of the recording head, head slider, and suspension is called a head gimbal assembly (HGA). An actuator positions the recording head over the specific track of interest. The actuator first rotates to seek the track of interest and after positioning the recording head over the track, maintains the recording head in close registration to that track. The disk in a disk drive has a substrate and a magnetic layer on the substrate for magnetic recording. The head slider carrying the recording head has a disk facing surface upon which an air bearing surface (ABS) is constructed. The ABS allows the slider to float on a cushion of air and to be positioned close to the disk surface. The head slider includes a fly-height control for adjusting the distance between the head slider and the magnetic disk. As the areal density of HDDs increases and the flying height of the head slider above the disk surface decreases, any head slider protrusion or contamination (particularly at the lowest flying portions of the head), may cause contact between the head slider and the magnetic disk. Contact between the recording head ABS and the disk can cause damage to the recording head and can also lead to wear failure at the interface between the recording head and the disk. If those drives most likely to fail can be screened out, the reliability and quality of the remaining drives can be increased. The current method of inspecting head slider surfaces using a scanning electron microscope (SEM), is not practical for testing each and every HGA, and other optical inspection techniques may miss microscopic protrusions or contamination that are still large enough to cause failures in the HDDs. It has been found, in fact, that head sliders with gross contamination that can be detected by SEM, can often not be detected by even 1000× optical screening.